We intend to map the cycles involving pyruvate in hepatocytes and kidney cortex tubules. We will use 14C labeled substrates, and steady state models solved with the aid of a microcomputer. Data required are isotopic yields in the major products as well as 14C distribution in products and key intermediates. The changes will occur with fasting or meal feeding high carbohydrate, and with hormonal (glucagon, epinephrine) pretreatment will be quantitated. Inhibitor titration will also be used to examine key rate-limiting steps.